The irradiation of a target volume in an irradiation volume of an object with ion beams or particle beams relates to the irradiation of matter, especially organic, inorganic and biological materials, and it is used in various fields of research, industry and medical technology. In this context, the target volume comprises particularly the region in which a prescribed dose is to be deposited in order to modify the irradiated material; in particular, the irradiation volume also encompasses those regions of the material that are penetrated by the radiation, whereby the desired dose is then applied to the target volume. The term “particle beam” or “ion beam” refers especially to a high-energy beam consisting either of charged particles such as, for example, protons, carbon ions or ions of other elements, pions or else of neutral particles such as, for instance, neutrons. In the description below, the terms “ion beam” and “particle beam” are used synonymously. High energy refers especially to the energy of the particles in the range from several MeV/amu to several GeV/amu (amu: atomic mass unit).
A radiation device that is suitable for performing the irradiation generally has an acceleration means that generates and shapes the ion beam, and, for purposes of the irradiation, said ion beam is conducted by means of a beam transport system into a region in which the irradiation volume is situated. Furthermore, the radiation device comprises a beam modification means that can adapt the parameters of the ion beam to the position and size of the target volume. In particular, the beam modification means is also referred to as an application system that specifies the energy, direction and fluence or dose of the ion beam in such a way that the dose distribution corresponds approximately to the position and size of the target volume.
The irradiation volume can be simulated, for example, by a detecting means that serves to verify an irradiation field. The irradiation volume generally comprises an irradiation field that is a field with a maximum extension in the lateral direction, in general in the x- and y-directions, and that lies perpendicular to the direction of the ion beam. Here, the detecting means can consist of a verification field or of a so-called stack with several laterally extended verification fields arranged one behind the other. In the realm of dosimetry, for example, films with a photographic emulsion are used. Moreover, core trace detectors are employed for measuring the fluence distribution in the irradiation field. In the realm of medical applications, the irradiation of biological tissue is used in order to study the effect of particle irradiation so as to be able to estimate the effect of exposure to cosmic radiation in outer space.
Finally, the target volume in the irradiation volume can also be the volume of a tumor in a patient. As a rule, the irradiation volume here is specified by the attending physician and it comprises the actual target volume, that is to say, the tumor volume, as well as a safety margin around the visible tumor volume. Ion beams are used here to destroy the tumor tissue within the irradiation volume.
In tumor therapy, the special properties of ion beams make it possible to expose the tumor tissue to a very high dose, yet with minimal damage to the surrounding healthy tissue. This is mainly due to the favorable depth-dose distribution of ion beams. When high-energy ion beams penetrate into the material, they initially deposit little energy. As the depth increases, the specific energy deposition rises, reaches its maximum in the area of a distribution curve referred to as a Bragg peak, and then drops sharply. As a result, even with deeper tumors, more energy can be deposited in the tumor tissue than in the surrounding healthy tissue. Moreover, for heavy ions such as, for example, carbon ions, the biological efficacy increases in the maximum of the Bragg peak.
The target volume is generally scanned one slice or one layer at a time in the direction of the particle beam (z-direction) in that the Bragg peak is shifted or scanned in the z-direction over the target volume. As a rule, this shift of the Bragg peak is carried out in that the energy of the particle beam is changed. In this process, the target volume is divided into so-called iso-energy layers, and the various iso-energy layers each have a differing energy of the particle beam. The lateral scanning of the target volume is generally carried out in that the particle beam scans an iso-energy layer in the x-, y-plane, preferably one dot at a time. The x-y plane is essentially perpendicular to the iso-energy layer in question. A scanning dot is generally referred to as a matrix dot, so that the target volume is divided into matrix dots, each with x-, y-, z-coordinate points that are preferably scanned consecutively and to which a specific dose of the particle beam is applied.
In this process, the body to be irradiated (especially a volume region inside the body that is to be irradiated) can be static/unmoving or moving. It can happen that the irradiation volume in the irradiated object or in parts thereof, especially the target volume that is to be irradiated, is moving. A movement can be made not only translatorily relative to an external coordinate system, but rather also in the form of a shift of various regions of the body that is to be irradiated relative to each other (including twisting and deformations).
In order to be able to irradiate intrinsically moving bodies, so-called four-dimensional irradiation methods are used. In actual fact, these are three-dimensional irradiation methods that have a time variation (with time as the fourth dimension). Examples of such material processing methods can be found in the realm of material sciences in the production of highly integrated components (especially microprocessors and memory chips) as well as in the production of microstructured and nanostructured mechanisms.
Scanning methods can be used. In particular, three specific approaches are discussed. These are so-called rescanning methods, gating methods and tracking methods.
In the case of rescanning methods, the body that is to be irradiated undergoes a large number of consecutive irradiation procedures. On the statistical average, a sufficiently strong irradiation of the target volume is achieved if the moving body (or the target region that is to be irradiated) has a cyclically recurring movement pattern. However, it is problematic that this almost unavoidably results in a relatively high radiation dosage of the partial regions of the target body that should, in fact, not be irradiated. Moreover, the principle of rescanning processes means that they lend themselves primarily for relatively fast, cyclically recurring movements.
In the case of gating methods, an active irradiation of the target body only takes place when the volume region that is to be irradiated is located in a relatively narrowly delimited, defined region. At other points of time, however, no irradiation occurs (as a rule, because the particle beam is switched off). Fundamentally, gating methods yield good irradiation results. A drawback, however, is the longer irradiation duration that, among other things, entails higher costs.
An especially promising approach is offered by the tracking methods. Here, the region that is exposed to the irradiation is tracked, corresponding to the movement of the volume region of the target body that is to be irradiated. Tracking methods combine the advantages of a precise, targeted treatment with relatively short irradiation times.
The success of tumor therapy based on irradiation of the target volume, and thus of the tumor, depends largely on the extent to which the effective part of the ion beam can be concentrated exclusively onto the target volume.
For this reason, it is desirable to know, as precisely as possible, the exact position of the ion beam in the target volume of an object during its irradiation.
A laminated gamma detector is shown in FIGS. 1 and 2 as well as on page 19, line 21 through page 21, line 14 of WO 2008/009528, which is incorporated by reference herein in its entirety. This reference describes a detection system in conjunction with searching for land mines that is direction-sensitive. Further, WO 2008/009528 describes, especially on page 23, line 28 through page 27, line 32, pertaining to FIGS. 3, 4 and 5, that electrons that strike obliquely will have less of a chance to deposit their energy into one plate.